Extract differences between an old default RoundCube config and its custom one, for pasting to the end of a much newer custom config file.

compare-roundcube-config.php

<?php

define("RCMAIL_VERSION", "RCMAIL_VERSION");
require 'defaults.inc.php';
$default_config = $config;
unset($config);
require 'config.inc.php';
$custom_config = $config;
unset($config);

// return elements of 1st array that are not in the 2nd or don't
// match it

function array_diff_assoc_recursive($array1, $array2) {
    $difference = [];

    foreach ($array1 as $key => $value) {
        if (is_array($value)) {
            // If the key doesn't exist or
            // isn't an array in the second
            // array
            if (!isset($array2[$key]) || !is_array($array2[$key])) {
                $difference[$key] = $value;
            } else {
                // Recursively find
                // differences in
                // nested arrays
                $new_diff = array_diff_assoc_recursive($value, $array2[$key]);
                if (!empty($new_diff)) {
                    $difference[$key] = $new_diff;
                }
            }
        } elseif (!array_key_exists($key, $array2) || $array2[$key] !== $value) {
            $difference[$key] = $value;
        }
    }

    return $difference;
}

$result = array_diff_assoc_recursive($custom_config, $default_config);

foreach ($result as $key => $value) {
    if (is_string($value)) {
        $value = "'" . $value . "'";
    }
    elseif (is_array($value) || is_bool($value)) {
        $value = var_export($value, true);
    }

    print('$config[' . "'" . $key . "'] = " . $value . ";\n");
}